1. Field of the Invention
This invention relates generally to devices and methods for setting fractured long bones of the body, such as arm and leg bones. More particularly, this invention relates to an improved intramedullary fixation rod for setting a fractured bone in a manner permitting limited elastic movement in response to natural stresses at the fracture site to avoid interference with the natural healing process.
2. Description of the Related Art
Long bones of the body are characterized by a combination of two different bone materials cooperating together to provide a relatively lightweight and high load bearing structure. More specifically, such bones consist of a relatively hard and generally tubular outer layer of cortical bone, sometimes referred to as the cortex, encasing a considerably softer and sponge-like inner bone material referred to as cancellous bone. Examples of such long bones in the human body are leg bones including the femur, tibia, and fibula, as well as arm bones including the radius, ulna, and humerus.
When a long bone is diaphyseally fractured, it is necessary to set the fracture by returning or reducing the adjacent broken bone ends at the fracture site to their original anatomical positions. The fractured bone is then restrained or fixed in the reduced position by an appropriate restraining device thereby permitting healing to proceed. The restraining device must be left in place at least until the fracture is substantially healed.
A variety of restraining devices and placement procedures therefor are known for maintaining diaphyseal fractures in long bones in a reduced position. For example, fixation plates have been used conventionally for many years and are placed surgically onto the bone in a position spanning the fracture site. Screws or other suitable attachment devices are fastened through the plate into the bone to lock the plate in position and thereby rigidly immobilize the fracture site for an extended period of time during which the bone is allowed to heal.
However, such fixation plates isolate the fracture site from natural stresses and interfere with callus formation, thereby interfering with the natural healing process. As a result, the cortical bone in the region of the fracture site tends to heal with undesirable cancellization of the cortical bone, thus providing a relatively weak bone structure subject to refracture. Furthermore, the formation of screw holes in the cortical bone provides stress risers which further substantially increase the risk of bone refracture. Moreover, relatively complicated surgical procedures are required for the implantation and subsequent removal of such fixation plates, thereby presenting significant risks of neurovascular injury and resulting in substantial emotional trauma to the patient.
Alternative fracture restraining devices have been proposed in the form of intramedullary fixation rods or nails for fixation of the bone fracture without requiring use of fixation plates. Such fixation rods have been provided in various lengths and cross-sectional shapes for insertion through the medullary canal of a fractured bone to support adjacent broken bone ends in alignment with each other during healing.
In general, these fixation rods fill the intramedullary canal and have substantial contact with the inner, or endosteal, surface of the cortical bone. This inhibits endosteal callus formation and revascularization of the bone by its endosteal blood supply.
Furthermore, these fixation rods have generally provided relatively poor rotational stability, particularly in response to any relative rotation between the broken bone ends, thereby tending to result in undesired rod loosening.
Moreover, these fixation rods have consisted of relatively rigid structures insertable only into relatively straight bones, such as the femur. These rods function to rigidly immobilize the fracture site throughout the healing process. This results in shielding the fracture from natural loading stresses and inhibiting callus formation, thus promoting a relatively poor healing of the fracture. Furthermore, fixation rods currently available have relationships between their bending and torsional rigidities which are substantially different from those of intact bone. This can result in rigid fixation in bending but unstable fixation in torsion.
Rods have been used through the medullary canal of a somewhat curved bone, such as the radius or ulna bones of the forearm. When installed, however, these fixation rods have functioned to straighten the fracture site, leading to malreduction or unsatisfactory positioning of the fracture fragments.
Therefore, a significant and important need exists for an improved device for reducing a diaphyseal fracture in a long bone in a manner which promotes callus formation and the natural healing process and allows normal endosteal healing. Furthermore, a need exists for such an improved device which can be installed or removed without complicated surgical procedures, which provides relatively high rotational stability and which can be used with curved bones, such as the radius or ulna of the forearm, as well as other long bones, such as the femur or tibia. The present invention fulfills these needs and provides further related advantages.